I have skied over 100 ski areas and Mammoth was one of the last major US ski areas that I had never skied until last weekend. I had a great time overall. About 8" of new snow fell while I was there and weather was a little bit of everything (sun, snow, wind, fog, thunder). Almost the entire mountain was skiable, the only exception being lifts 9, 22 and 25 (and a few real estate lifts)
I had high expectations for Mammoth and IMO it's a real good mountain but not great. Pros/cons:
PRO: great upper mountain, wide open bowls.
PRO: 2 steep groomers off the upper mountain
PRO: good size (although both vert and acre numbers seem to be exaggerated significantly, 2900' and 2800 acres seems more accurate)
PRO: more open runs in the late spring than just about anywhere
PRO: great views, you can see for miles
CON: short runs. None of the open chairlifts exceeded 1100' vert, several lifts half that (closed chairs 22 and 9 are longer at about 1500'; gondola 2k)
CON: Lower mountain flat. There are a few short blue or black pitches (200-400' vert), but most of the lower mountain is green/easy blue.
CON: Skiable runs closed. I'm not sure why, but lots of runs with good snow that were accessible by open lifts were closed.
CON: Odd lift management. Lifts 1, 6, 11 and the lower gondola all serve the same runs and all were running. Why not close one of these lifts and open another area. It would spread people out more and open more runs. They also had the backside lifts closed, lots of people skied them and staff was very nice to tow some of the people with snowmobiles, but why not use that staff to just open the lift.
CON: crowded/hard to get to. For an area that is so hard to get to, it's still fairly crowded. If I lived locally, I'd ski Mammoth all the time though.
lift 23 was the best area